In cabinet making and other carpentry work, there is a frequent requirement to use a router to cut grooves or slots which are parallel to an edge of a work piece including a rabbet groove in the edge itself. It is highly desirable that such grooves be located and cut with precision in order to facilitate subsequent assembly operations utilizing the work piece. Heretofore, considerable time has usually been required on the part of the workman to obtain such precision-cut and positioned grooves. Further, there has been difficulty in having the grooves completely straight at opposite ends. Still further, it has usually been necessary to interchange bits when going from cutting a narrow groove to cutting a wider groove.
U.S. Pat. No. 3,478,788 granted to H. J. Zelik on Nov. 18, 1969 discloses a router attachment of a general type that has been used to enable workmen to cut grooves in a workpiece which are parallel to a straight edge on the workpiece. However, attachments of this prior art type require considerable time and skill on the part of the workman in order to set a guide so that a groove is cut in the proper location. Usually, some trial-and-error manipulations are involved in the setting. Further, when using attachments of the type disclosed in the Zelik patent considerable difficulty is involved in forming grooves which are completely straight at opposite ends. Other patents disclosing router attachments for the same general purpose include: U.S. Pat. No. 4,044,805 to D. D. Gronholz dated Aug. 30, 1977; U.S. Pat. No. 4,685,496 to L. R. Livick dated Aug. 11, 1987; U.S. Pat. No. 4,718,468 to G. W. Cowman dated Jan. 12, 1988 and U.S. Pat. No. 4,776,374 to B. Charlebois dated Oct. 11, 1988.